With the promotion and popularization of digital imaging technologies, optical imaging devices are widely used in various types of equipments, such as a variety of portable and small equipments. Miniaturized optical imaging devices, such as small zoom lenses, are widely needed.
The existing small zoom lens generally includes a focus driving mechanism and a zoom driving mechanism which are used to drive corresponding lens groups to move to achieve focus and zoom, respectively.
Voice coil motor (VCM) is a relatively simple motor. Specifically, a linear voice coil motor is widely used in the optical field, such as in an auto focus module of a camera of a cell phone. For clarity, the moving part of the voice coil motor is referred to as focus mover assembly and the relatively fixed part is referred to as focus stator assembly hereinafter.
A basic structure of a voice coil motor is shown in FIG. 1, which generally includes a stator 1a1, a mover 1a2 and an elastic connection member 1a3. The elastic connection member connects the mover and the stator. A load (not shown) is fixedly mounted at the mover. In FIG. 1, the stator is a permanent magnet, and the focus mover assembly includes a driving coil 1a23 wound on the mover. After the driving coil is supplied with power, the mover is linearly moved under the action of the magnetic field of the stator. A movement of the mover in an opposite direction may be achieved by supplying a reverse current to the driving coil or utilizing the restoring force of the spring. In other examples, it is also possible that the mover is a permanent magnet and the driving coil is included in the focus stator assembly.
The voice coil motor with the structure described above may precisely position the location of the load (for example, move a focus lens to a desired position) by the balance between the electromagnetic force generated by the driving coil and the elastic force of the elastic connection member. In general, the elastic force of the elastic connection member is proportional to the displacement thereof in a working range, which leads to that the larger the displacement of the mover, the larger the electromagnetic force required, and the larger the current required for driving the driving coil. In a case that the mover needs to be kept at a fixed position (for example, a position for focusing) for a long time, the current required for driving the driving coil also needs to be maintained for a long time, which leads to a larger static holding power consumption of the voice coil motor.